Control circuits for cathode-ray apparatus



Sept. 9; 1947.V J. M. lzonps ETAL 2,427,263

CONTROL CIRCUITS FOR CATHODE RAYVAPPARATUS 'Filed sept. 21. 1943 Ry. fz

' INVENTOR 2H Ziw T W? ATTORNEYS Patented Sept. 9, 1947 CONTROL CIRCUITS FOR CATHQDE-RAY APPARATUS ohn Mathieson Dodd John S'coles, East assignors to Metro Company Limited, London,

.pany of Great Britain Application September 21 In Great Britain Section 1, Public Law 690, August 8,1946. Patent expires August 8, 1961 (Cl. Z50- 20) 3 Claims.

This invention relates to means for deflecting a cathode ray beam, either recurrently or to a controllable position, at will. The invention has special but not exclusive application in panoramic radio receivers the nature of which was described in Electronics June 1940, and wherein, in brief, a waveband, or it may be any selected one of a plurality of wavebands, is scanned from end to end by the automatic variation of a tuning parameter at a rate comparable with the frequency of the persistence of vision, the output or outputs due to any received radio transmissions which may be taking place within the waveband being, indicated as resonance or peak components perpendicular to a time base waveband component on the screen of a cathode ray tube, the time base component being provided synchronously with the scanning such as by means of a saw-tooth type of oscillation generator. Provision can be made whereby any selected one off the thus indicated transmissions can be tuned into manually and its modulation listened to or recorded or otherwise indicated, that is to say, the scanning of the waveband can be effected solely by hand such as through the turning of a knob about an associated dial indicating the wavelength. In such a panoramic receiver it has been convenient for the purpose of the rapid scanning of the waveband to wobble the value of certain tuning components of the oscillator section of a frequency changer valve in a superheterodyne, circuit. It is known in such a panoramic receiver to eifect the rapid scanning by means of a so-called reactor valve in one form of which the eiective or apparent grid-cathode capacity of the valve is varied by varying the potential of the grid such as by means of a sawtooth voltage generator, this reactor valve having a atly tuned anode circuit and having its gridcathode circuit connected in parallel with a sharply tuned inductance-capacity circuit of the oscillator stage of the frequency changer which may be the second frequency changer in a circuit wherein there are in all three frequency changers with associated respective local oscillators; According to U. S. application Serial No. 503,281, filed September 21, 1943, the output of the oscillator with which the reactor valve is associa-ted inparallel is applied to the grid of a high frequency amplier valve having a atly s, Timperley, and Graham Sheen, London, England, politan-Vickers VElectrical England, a com- 1-943, Serial No. 563,277

August 8, 1941 tuned anode circuit, and the output of thisy amplier valve is applied Vto the frequency changer.

The present invention comprises a specic arrangement conveniently enabling changeover from automatic scanning to hand scanning when magnetic deflection of the cathode ray beam is employed.

According to the invention means for magnetically delecting the beam of a cathode ray tube, either automatically recurrently, or to a manually controllable position, at will, comprise a source of recurrently varying voltage or current supplying at least one deflection coil and itself supplied from one source of operating power through a common busbar to which is connected the cathode circuit of a reactor valve for concomitantly andA correspondingly electing tuning scanning of another device (such as a panoramic radio receiver) providing a video output to be observed on the cathode ray tube, which reactor valve has its anode circuit supplied from a second operating power source the negative terminal of which is connected to said common busbar, whilst the grid of said reactor valve is supplied with the recurrent voltage (preferably through an ampliiier) whilst furthermore switching means are provided for cutting off the recurrent voltage from the system and for connecting the grid of said reactor valve (preferably through the above indicated amplifier if provided) to a manually variable source of potential such as a potential divider. tooth oscillation generator and the reactor valve are fed from respective power supplies suchthat the positive busbar of the former and the negative busbar ofthe latter are common and may conveniently be earthed, the saw-tooth Voltagev or current being conveniently supplied Via a variable potential divider and a series resistor to the grid of one of a pair of amplifier valves, which may conveniently be directly coupled ln push-pull in per se known manner such as by means of a common cathode resiston, and inthe anode circuits of each of which valves is a deflection coil and a resistor in series, the two resistors being connected to' the common busbar. This particular arrangement ensures that the voltage drop across the resistors follows exactly the current flowing throughA the coils andl soa potential divider across the ends, remote from Thus the saw- 3 the common busbar, of the two resistors enables an adjustable voltage proportional to the coil current, that is, to the time-base deflection of the receiver, to be applied to the grid of the reactor valve and thus to alter the tuning of the radio receiver synchronously with the movement of the cathode ray beam by the saw-tooth current flowing in the deflection coils. The means whereby whenever desired the saw-tooth oscillator can be switched off and the grid of the first of the aforesaid amplifier valves connected directly to the tapping on the potential divider permits that, by adjusting this potential divider, the receiver can be manually tuned to any desired signal Within the waveband while the cathode ray beam indicates the corresponding otherwise exactly as when lator is in operation.

The use ovf the aforesaid push-pull amplifier is preferred for reasons associated with the magnetic deflection of cathode ray beams, but it is in the saw-tooth oscilno way essential to the invention, the important f electrical circuit diagram illustrating the invenv tion.

Figure 2 is a detail view of the reactor valve and its circuits.

In the drawing the rectangle I represents the saw-tooth voltage generator or other means whereby the cathode ray beam is deflected recurrently according to a, predetermined law such as, more particularly, to provide the time base and whereby concomitantly to effect the scanning of the radio receiver of the panoramic type.

In the preferred circuit arrani'gement illustrated the ouput from the device I, which will be hereinafter. for convenience referred to as the saw-tooth voltage generator, is fed through the condenser 2, the tapping point 3 of the potentiometer 4 (which may be adjustably preset) and through the series resistance 5 to the control grid of an amplifier valve 6 having push-pull association with an amplifier valve 1, these valves having the common cathode resistor 3. As resistance 2l is very small in comparison with resistance 4, the grid of valve 1 has effectively no voltage variation applied to it. The anode circuit of th'e valve 6 has the cathode ray tube deflector coil I l in series with a resistance I2 connected to the common" busbar I3. The anode circuit of the valve 1 has the complementary deflecting coil i4 in series with the resistor I5 also connected to the conmion busbar I3.

The common busbar I3 is preferably earthed as indicated at I6 and is connected withl the positive terminal of a source of power supply indicated by the rectangle I1 for the saw-tooth generator I and amplifier valves 6 and 1, the negative terminal of this source being connectedto what may be called for convenience the cathode busbar I8 of the saw-tooth generatorY I and valves 6 and 1. TheY bias of these valves in the circuit illustrated is conveniently determined-in part by.

position on the screenv 4 the tapping I9 between the resistances 20 and 2l connected in series across the source I1.

The rectangle 22 in Fig. 1 indicates the reactor valve th'e arrangement of which, along with the oscillator of the second frequency changer stage, is similar to that illustrated in the drawing of U. S. Patent No. 2,383,420, granted August 21, 1945. In the arrangement of this valve as shown in Fig. 2, V2 is the oscillator valve having a resistance R2 in its anode circuit, the output of this valve being passed to the mixer valve inknown manner or through an intervening amplifier as described in application Ser, No. 503,281 aforesaid, and VI is the reactor valve. Due to the feed-back coil L2 and valve V2, oscillations appear in circuit LI, C I, across which is the gridcathode circuit of valve VI. The anode circuit of valve VI is effectively resistance R coil L3 being provided merely to tune out the stray capacitance, while C2 is a very small trimming condenser to enable the optimum tune to be ob- I tained. As resistance of R is small, the anode circuit is very fiat and, being predominantly resistive, the voltage appearing at the anode is approximately in anti-phase with that on the grid over a wide range of frequency. The frequency to which the circuit through the condenser C3 is resonant is altered by varying the bias voltage applied to the grid of valve VI by means of the circuit shown in Fig. l. The saw-tooth voltage input to the reactor valve is taken from the adjustably preset tapping 24 on the potentiometer Z5 connected across the respective lower ends of the resistances I2 and I5. The cathode circuit of the reactor valve arrangement 22 is connected to th'e common busbar I3, and the anode circuit of this valve and conveniently also of the local oscillator and amplifier associated therewith` is supplied from the source 26 which is separate and distinct from the source I1 and which has its negative terminal connected to the common busbar I3. The power supply to the saw-tooth generator I is taken from the common busbar I3 through th'e manual switch 21 so that the automatic scanning or time base provision may be cutout when desired, and to enable the handscanning to be eifected a manual switch 28 is provided which is connectedto the control grid of thev valve il through the resistor Y2.13, the other terminal of the switch being connected to the manually operable slider 30 on th'e potentiometer 3|, which is conveniently connected between'the common busbar I3 and the cathode busbar I8, the Yarrangement being such that when the normally open switch 28 is closed, by movement of the slider 30 manual scanning can be accurately effected otherwise Vin correspondence with the normal automatic scanning.

We claim: Y Y

i. The combination of a radio receiver providing a video output to' be observed on Ya cathode ray tube, complemental coils for magnetically defiecting the` beam of th'e cathode ray tube,V a power system embodying a first source of operating power and a second source of operating power, a busbar common to said sources of operating power and connected to the negative terminal of said second source of operating power, a source of recurrently varying voltage supplied from one of said sources of operating power through said busbar and supplying said beam defiecting coils,

a frequency varying reactor valve having an ancomitantly and correspondingly effecting tuning scanning of the receiver, an anode circuit for said reactor valve connected to said second source of operating power, and a grid circuit for said reactor valve having means for supplying it with said recurrently varying voltage, a manually variable source of potential, and switching means for disconnecting said source of recurrently varying voltage from the system and for connecting the grid of said reactor valve to said manually Variable source of potential.

2. The combination according to claim 1, including a pair of push-pull amplifying Valves having anode circuits connected to the complementary beam deflecting coils for the cath'ode ray tube, and a potential divider for connecting said coils to the grid of said reactor valve.

3. The combination according to claim 1, including a pair of push-pull amplifying valves having anode circuits connected to the complementary beam deflecting coils for the cathode ray tube, a potential divider for connecting said coils to the grid of said reactor valve, a potentiometer connected across a suitable source of potential, and means including a switch and a slider for connecting the grid of one of said amplifying Valves to said potentiometer.

JOHN MATHIESON DODDS. GRAHAM JOHN SCOLES.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

